Noise-Reducing Extrusion Coating Compositions

ABSTRACT

Methods for extrusion coating a substrate are provided. The methods comprise applying an extrusion coating composition to a surface of a substrate by extrusion coating. In these methods, the extrusion coating composition includes a polyolefin and an inorganic particulate material having an average particle size of no greater than 2 μm and a particle loading of at least 20 weight percent, based on the total weight of polyolefin and the inorganic particulate material.

BACKGROUND

The extrusion coating process can be described as the application of amolten polymeric web onto a moving substrate at high melt temperaturesand generally high speeds of up to over 700 meters per minute (mpm).Extrusion coating aimed at producing high gloss surface finishes fordecorative purposes create a lot of noise in the area around thelaminator, which often requires additional precautions for a safeoperating environment in terms of common industrial hygiene standards.The noise represents an indicator for process related limitations, whichare becoming more accentuated with increasing line speeds. However, highline speeds are desirable because they enable economically attractiveoperation of extrusion coating equipment. Therefore, it would be helpfulto have a robust extrusion coating process free of edge over-coatingproblems (i.e., sticking to the pressure or chill roll) that lead toprocess disruptions, including loss of over-coating and destruction ofpolymer adhesion.

SUMMARY

One aspect of the invention provides methods for extrusion coating asubstrate, the methods comprising applying an extrusion coatingcomposition to a surface of the substrate by extrusion coating, wherebythe extrusion coating composition contacts a chill roll surface. In themethods, the extrusion coating composition comprises a polyolefin and aninorganic particulate material having an average particle size of nogreater than 2 μm and a particle loading of at least 20 weight percent,based on the total weight of the polyolefin and the inorganicparticulate material in the coating composition. In some embodiments ofthe methods, the polyolefin comprises a polyethylene or polyethyleneinterpolymer having a density of no greater than 940 g/cc.

In some embodiments of the methods, the extrusion coating compositionsis characterized in that it reduces the extrusion coating noise level atthe chill roll release point by at least 3 dB relative to an identicalextrusion coating process conducted with the same extrusion coatingcomposition absent the inorganic particulate material. For the purposesof this disclosure, noise reduction is measured for a polyolefinextrusion coatings composition applied on a chrome-plated glossy chillroll with a surface roughness of 0.5 μm, at an extrudate temperature atthe die of 320° C. and an air gap of 250 mm at a coating weight of 25(g/m ²) and a line speed of 300 mpm or at a coating weight of 12 g/m² ata line speed of 500 mpm. In some embodiments the extrusion coatingcompositions is characterized in that it reduces the extrusion coatingnoise level at the chill roll release point by at least 10 dB. Theextrudate temperature can be measured using an infrared radiationthermometer focused on the extrudate just as it leaves die.

In some embodiments of the methods, the inorganic particulate materialhas an average particle size of no greater than 1.5 μm and a particleloading of at least 30 weight percent, based on the total weight of thepolyolefin and the inorganic particulate material in the coatingcomposition. The inorganic particulate material can be calciumcarbonate.

Another aspect of the invention provides coated substrates comprising asubstrate and a coating composition coated on a surface of thesubstrate, the coating composition comprising a polyolefin and aninorganic particulate material having an average particle size of nogreater than 2 μm and a particle loading of at least 20 weight percent,based on the total weight of the polyolefin and the inorganicparticulate material.

In some embodiments, the substrate comprises a paper product.

In some embodiments, the inorganic particulate material has an averageparticle size of no greater than 1.5 μm and a particle loading of atleast 25 weight percent, based on the total weight of the polyolefin andthe inorganic particulate material.

In some embodiments, the polyolefin comprises a polyethylene orpolyethylene interpolymer has a density of no greater than 940 g/cc andthe inorganic particulate material comprises a mineral.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a schematic illustration of a side-view of a system forextrusion coating a substrate.

FIG. 1( b) is a schematic illustration of the top view of the system ofFIG. 1( a).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The inventors have unexpectedly discovered that by adding an inorganicparticulate material having an appropriate particle size distribution atan appropriate loading to a polyolefin in an extrusion coatingcomposition, excellent chill roll release, and therefore substantiallyreduced noise, can be achieved without degrading the adhesion betweenthe extrusion coating and the coated substrate.

As such, one aspect of the invention provides methods for extrusioncoating a substrate, the methods comprising applying an extrusioncoating composition to a surface of a substrate by extrusion coating. Inthese methods, the extrusion coating composition includes a polyolefinand an inorganic particulate material having an average particle size ofno greater than 2 μm and a particle loading of at least 20 weightpercent, based on the total weight of the polyolefin and the inorganicparticulate material.

Without intending to be bound to any particular theory of the invention,it is believed that a particulate material having the appropriateparticle size distribution and loading provides an extrusion coatingwith a sufficient number of inorganic particles at the interface of theextrusion coating and the chill roll surface during the extrusionprocess to substantially reducing the sticking of the extrusion coatingto the chill roll, without degrading the adhesion between the extrusioncoating and the coated substrate.

Polyolefins:

The extrusion coatings include at least one polyolefin. “Polyolefin”,“PO” and like terms mean a polymer derived from simple olefins.Representative polyolefins include polyethylene, polypropylene,polybutene, polyisoprene and their various interpolymers. The presentmethods are particularly well-suited for use with extrusion coatingsthat include polyolefins, such as polyethylene of lower densities andinterpolymers (e.g., copolymers) thereof, because such polyolefins areknown to experience substantial tackiness on chill rolls duringextrusion coating and, therefore, to produce a lot of noise.

The polyolefins can be, for example, low density polyethylene (LDPE),polypropylene (PP), high density polyethylene (HDPE) and otherpolyolefins of lower densities such as enhanced polyethylene (EPE),polyolefin plastomers (POPs), polyolefin elastomers (POEs),polypropylene based plastomers (PBP) and polyolefin block elastomers(PBEs), such as olefin block copolymers (OBCs). Suitable polyolefins oflower densities include ultra low linear density polyethylenes (VLDPEs),including metallocene polyethylenes and polyethylene copolymers. Thecomonomers that are useful in the preparation of polyethylene copolymersinclude alpha-olefins, such as C₃-C₂₀ alpha-olefins (e.g., C₄-C₁₀alpha-olefins). The alpha-olefin comonomers can be linear or branched,and two or more comonomers can be used, if desired. Examples ofpolyethylene copolymers include ethylene acrylic acid (EAA) copolymers,ionomers, ethylene methyl acrylic acid (EMAA) copolymers, ethylene ethylacrylate (EEA) copolymers, ethylene methyl acrylate (EMA) copolymers,ethylene butyl acrylate (EBA) copolymers, and ethylene vinyl acetate(EVA) copolymers.

The polyolefins used generally have a density of no greater than about0.940 g/cc. This includes embodiments in which the polyolefin is apolyethylene having a density of about 0.916 Wee to about 0.940 g/cc andfurther includes embodiments in which the polyethylene has a densitybelow 0.916 g/cc (e.g., from about 0.860 g/cc to about 0.915 g/cc). Insome embodiments the polyolefins, including polyethylene and/orpolypropylene, have a density of from about 0.860 g/cc to about 0.905g/cc. This includes embodiments in which the polyethylene and/orpolypropylene have a density of from about 0.860 g/cc to less than 0.890g/cc. For the purposes of this disclosure, densities are measured inaccordance with ASTM D-1505.

The present extrusion coating compositions typically have a polyolefincontent of up to about 80 weight percent (wt. %), based on the totalweight of the polyolefin and the inorganic particulate material in theextrusion coating composition. This includes embodiments in which theextrusion coating compositions have a polyolefin content of up to about75 wt. %, based on the total weight of the polyolefin and the inorganicparticulate material in the extrusion coating composition.

Inorganic Particulate Material:

The inorganic particulate material can take the form of a wide varietyof materials, provided that it has the noise-reduction capabilitiesdescribed herein. Generally, any minerals that can be ground to a fineparticle size less than the thickness of the coatings and is stableduring the extrusion coating process without interaction with thepolymer can be used. In some embodiments, the particulate materialcomprises a mineral, such as calcium carbonate.

The particles in the inorganic particulate material have an averageparticle size (d50) of no greater than about 2 μm. In some embodiments,the particles of the particulate material have and average particle sizeof no greater than about 1.5 μm. The particles sizes presented in thisdisclosure are measured using light scattering on an ached material.

The inorganic particulate matter is present at a loading of at least 20wt. %, (e.g., about 20 to about 60 wt. %), based on the total weight ofthe polyolefin and the inorganic particulate material in the extrusioncoating composition. This includes embodiments in which the inorganicparticulate matter is present at a loading of at least 25 wt. %, basedon the total weight of the polyolefin and the inorganic particulatematerial in the extrusion coating composition.

Multilayered Coatings and Pre-Treatments:

In some embodiments, the extrusion coating compositions are co-extrudedwith one or more optional, additional extrusion compositions to providea multilayered, extrusion coated substrate, provided that the presentextrusion coating compositions are co-extruded as the outer layer incontact with the chill roll. Alternatively, the additional layers of amultilayered coated can be produced by an extrusion lamination process.Examples of polymeric materials that can be co-extruded or laminated toprovide a multilayered extrusion coating include, polyolefins,polyamides and polyesters.

In order to enhance the bonding of the extrusion coating to theunderlying substrate or the various layers of a multilayered coating toeach other, the coating layers and/or substrate may be pretreated. Forexample, extrusion coating and extrusion lamination processes can usecorona treatment, flame retardant or plasma treatment of the substratesor lamination webs or ozone treatment of the molten extrusion coatingcomposition to enhance interlayer adhesion.

Optional Components:

In addition to the polyolefin and the inorganic particulate material,the extrusion coating compositions can include other additives, such asthose typically found in extrusion coating compositions. These include,for example, stabilizers, flame retardants, fillers, slip and antiblockagents, and the like. When present, such additives typically accountfrom less than about 2 wt. % of the extrusion coating composition. Insome embodiments, the extrusion coating compositions are free ofparticulate fillers, other than the above-described noise-reducinginorganic particulate fillers.

Substrates:

Substrates that can be extrusion coated using the present methodsinclude papers, paperboards, polymeric films, metal foils, metalizedpolymeric films, SiO, coated films, woven and non woven fibers or tapesand the like. In some embodiments, the inorganic particulate material inthe coating result in enhanced adhesion to the substrate compared to anequivalent coating which does not include the inorganic particulatematerial. This enhancement can be measured, for example, using a peeltest.

Extrusion Coating:

A schematic illustration of a system for extrusion coating is providedin FIGS. 1( a) and (b). In its basic embodiment, extrusion coating is aprocess in which an extrusion coating composition is extruded from a die100 as a molten web 102 onto a moving substrate 104 which issubsequently passed through a nip 106 defined by a pressure roller 108and a chilled roller (“chill roll”) 110, which cools the molten web intoa solid polymeric coating 112 on the substrate.

In the extrusion coating process, as the polymeric coating is pulledfrom the chill roll, the noise intensity (chatter) generated at therelease point 114 is an indication of chill roll release. The lower thenoise level, the better the chill roll release.

In the present methods the extrusion coating compositions that areextrusion coated onto a substrate provide a noise level at the chillroll release point that is significantly reduced relative to that for anidentical method and extrusion coating composition in the absence of theinorganic particulate material. In some embodiments, the noise level atthe chill roll release point is reduced by at least 3 decibels (dB)relative to that for an identical method and extrusion coatingcomposition in the absence of the inorganic particulate material. Thisincludes embodiments in which the noise level at the chill roll releasepoint is reduced by at least 5 dB, at least 10 dB, or even at least 15dB, relative to that for an identical method and extrusion coatingcomposition in the absence of the inorganic particulate material.

Although the noise level of the extrusion coating process can depend onthe type of chill roll surface and material of construction, the presentcoating compositions and methods can be used to achieve a noisereduction on a variety of different chill roll surfaces, includingglossy, matte, and embossed chill rolls made with different surfaceplating materials such as chromed and the like.

EXAMPLE

This example illustrates one embodiment of a method of extrusion coatinga filled polyolefin composition onto a Kraft paper substrate.

The reduction in noise at the chill roll release point can depend on thesurface roughness of the chill roll and the line speed. Thus, for thepurposes of this disclosure and these examples, noise reduction ismeasured for 25 g/m² coatings at 300 mpm line speed and 12 g/m² coatingsat 500 mpm line speed onto Kraft paper against a glossy chrome platedchill roll with a surface roughness RT equal to 0.3 to 0.5 microns. Inmaking the comparison between the noise level produced by the presentextrusion coating compositions and a comparative extrusion coatingcomposition that does not include the noise-reducing inorganicparticulate matter, all other extrusion coating parameters that affectthe noise level at the chill roll release point are kept the same duringthe testing of both samples.

The extrusion coating compositions are prepared, for example, by dryblending a particle-filled compound (i.e., a master batch, MB) and thepolyolefins. Filled compounds include a high loading of the inorganicparticulate material in a carrier resin. The filled compounds areproduced through a compounding extruder, compounding on a milling rollor in a Banbury mixer, or by any other suitable method whereby thefiller and the carrier resin can be blended together to create ahomogeneous dispersion suitable for use in the extrusion coatingcompositions. The characteristics of each filled compound are listed inTable 1.

TABLE 1 Master Batches Com- Com- Particle size Filler pound poundCarrier Filler distribution Loading density Name Resin Type d50 wt. %g/cc MB1 LDPE PG7008 CaCO₃ 1.6 70 1.706 MB2 LDPE PG7008 CaCO₃ 1.3 701.706 Comparative Borealis Talc 6.5 30 1.15 CA8200

Two working master batches (MB1 and MB2) are prepared for use in theextrusion coating compositions of this example. Two types of calciumcarbonate mineral filler from Imerys are used in the master batches. Thefillers used are surface modified ultra-fine wet marble sold under thetrademark Supercoat®. The difference between the two calcium carbonatestested is the particle size distribution. A comparative filled compoundfrom Borealis is also tested. Borealis CA8200 is a talc filled compound.

Examples of suitable polyolefins used in the extrusion coatingcompositions are shown in Table 2 and the formulations for inventive andcomparative extrusion coating compositions are shown in Table 3.

TABLE 2 Melt flow index Density (g/10 min @ (g/cc) Poly- Polymer 190°C., 2.16 kg) ASTM mer Sold As: Type ASTM 1238-04 D792-00 PE LDPE PGPolyethylene 4.1 0.9215 7004 Homopolymer POP AFFINITY ™ Polyethylene 7.50.9020 PT1451G1 Plastomer EPE1 ELITE ™ Enhanced 12 0.911 5800Gpolyethylene EPE2 ELITE ™ Enhanced 8 0.918 5810G polyethylene

For the purposes of this disclosure, extrusion coatings are processed onan extrusion coating line (e.g., a Davis Standard (Erwepa) coating line)onto a chrome plated glossy chill roll having a diameter of 900 mm, asurface roughness (RT) equal to 0.3 to 0.5 microns. The extrusioncoating processing conditions are as follows. The set melt temperaturefor the extrusion coatings is 320° C. The air gap is 250 mm and the nipoff-set is 15 mm toward the pressure roll. The line speeds for theextrusion coatings are 300 mpm for 25 g/m² coatings and 500 mpm for 12g/m² coatings.

Noise measurements were made using a Realistic™ sound level decibelmeter (Tandy Corp.) at a defined position, representing the workenvironment for operators standing next to the laminator duringprocessing. The set-up for measuring the noise of the extrusion coatingprocess is shown in FIG. 1( b). The meter 116 is adjacent the releasepoint from the chill roll and pointed directly at the source of thenoise defined by the chill roll release point. For the purposes ofmeasuring the noise and evaluating any noise reductions, the distancebetween the noise meter 116 and the centerline 118 of the substratewidth 120 (shown as an ‘x’ in FIG. 1( b)) is 1200 mm. Measurements arepreformed under weighting selector ‘A’ responding to a frequency rangefrom 500 to 10,000 Hz. The results of the noise measurements areprovided in Table 3.

TABLE 3 Noise levels at the chill roll release point in dB. ExtrusionCoatings (Extrusion Temperature; Coating weight in g/m² (gsm); LineSpeed in mpm) Extrusion Coatings Extrusion Coatings (320° C.; 25; 300)(320° C.; 12; 500) PE 96 96 Borealis CC7290 88 91 POP 96 100 EPE1 99 93EPE2 91 94 60% POP + 40% MB1 81 92 60% EPE1 + 40% MB1 82 90 60% EPE2 +40% MB1 80 87 60% EPE2 + 40% MB2 79 86

(A reduction by 3 dB equals a noise reduction of 50%. The percentagesrepresent weight percent of the master batch in the extrusion coatingcompositions, based on the total weight of the master batch and thepolyolefin.)

All references to the Periodic Table of the Elements refer to thePeriodic Table of the Elements published and copyrighted by CRC Press,Inc., 2003. Also, any references to a Group or Groups shall be to theGroup or Groups reflected in this Periodic Table of the Elements usingthe IUPAC system for numbering groups. Unless stated to the contrary,implicit from the context, or customary in the art, all parts andpercents are based on weight and all test methods are current as of thefiling date of this disclosure. For purposes of United States patentpractice, the contents of any referenced patent, patent application orpublication are incorporated by reference in their entirety (or itsequivalent US version is so incorporated by reference) especially withrespect to the disclosure of synthetic techniques, product andprocessing designs, polymers, catalysts, definitions (to the extent notinconsistent with any definitions specifically provided in thisdisclosure), and general knowledge in the art.

Numerical ranges include all values from and including the lower and theupper values, in increments of one unit, provided that there is aseparation of at least two units between any lower value and any highervalue. As an example, if a compositional, physical or other property isfrom 100 to 1,000, then the intent is that all individual values, suchas 100, 101, 102, etc., and sub ranges, such as 100 to 144, 155 to 170,197 to 200, etc., are expressly enumerated. For ranges containing valueswhich are less than one or containing fractional numbers greater thanone (e.g., 1.1, 1.5, etc.), one unit is considered to be 0.0001, 0.001,0.01 or 0.1, as appropriate. For ranges containing single digit numbersless than ten (e.g., 1 to 5), one unit is typically considered to be0.1. These are only examples of what is specifically intended, and allpossible combinations of numerical values between the lowest value andthe highest value enumerated, are to be considered to be expresslystated in this disclosure.

Definitions:

“Polymer” means a polymeric compound prepared by polymerizing monomers,whether of the same or a different type. The generic term polymer thusembraces the term homopolymer, usually employed to refer to polymersprepared from only one type of monomer, and also embraces the terminterpolymer. “Interpolymer” means a polymer prepared by thepolymerization of at least two different types of monomers. This genericterm includes copolymers, usually employed to refer to polymers preparedfrom two different types of monomers, and polymers prepared from morethan two different types of monomers, e.g., terpolymers, tetrapolymers,etc.

“Composition”, “formulation” and like terms means a mixture or blend oftwo or more components.

The term “comprising” and its derivatives are not intended to excludethe presence of any additional component, step or procedure, whether ornot the same is specifically disclosed. In order to avoid any doubt, anyprocess or composition claimed through use of the term “comprising” mayinclude any additional steps, equipment, additive, adjuvant, or compoundwhether polymeric or otherwise, unless stated to the contrary. Incontrast, the term, “consisting essentially of” excludes from the scopeof any succeeding recitation any other component, step or procedure,excepting those that are not essential to operability. The term“consisting of” excludes any component, step or procedure notspecifically delineated or listed. The term “or”, unless statedotherwise, refers to the listed members individually as well as in anycombination. In the embodiments of this invention described herein,those embodiments described as “comprising” or “including” certaincomponents, steps, elements, etc. can be converted into additionalexamples by replacing the term “comprising” or “including” with thephrases “consisting of” or “consisting essentially of”.

Although the invention has been described in considerable detail throughthe preceding description, drawings and examples, this detail is for thepurpose of illustration. One skilled in the art can make many variationsand modifications without departing from the spirit and scope of theinvention as described in the appended claims.

1-10. (canceled)
 11. A coated substrate comprising: (a) a substrate; and(b) a coating composition coated on a surface of the substrate, thecoating composition comprising: (i) a polyolefin; and (ii) an inorganicparticulate material having an average particle size of no greater than1.5 μm and a particle loading of at least 25 weight percent, based onthe total weight of the polyolefin and the inorganic particulatematerial.
 12. The coated substrate of claim 11 in which the substratecomprises a paper product.
 13. The coated substrate of claim 11 in whichthe polyolefin is one or more ethylene-based polymers having a densityof no greater than 0.940 g/cc and selected from the group consisting ofpolyethylene homopolymers and polyethylene copolymers prepared from onlytwo different monomers.
 14. The coated substrate of claim 13, whereinthe coating composition consists essentially of the polyolefin andinorganic particulate material.
 15. The coated substrate of claim 11 inwhich the inorganic particulate material has a particle loading of atleast 30 weight percent, based on the total weight of the polyolefin andthe inorganic particulate material.
 16. The coated substrate of claim 11in which the polyolefin comprises a polyethylene or polyethyleneinterpolymer having a density of no greater than 0.940 g/cc and theinorganic particulate material comprises a mineral.
 17. The coatedsubstrate of claim 11, further comprising one or more additional coatinglayers disposed between the substrate and the coating composition. 18.The coated substrate of claim 11, wherein the inorganic particulatematerial is calcium carbonate.